The present invention relates to a nonlinear energy sink and to the use of same to improve the sound insulation between two spaces that are separated by a wall.
The sound insulation between two rooms that are separated by a wall is typically provided either by increasing the density of the wall or by lining said wall. In the case of two-leaf partition walls, a sound insulating material, typically a mat of mineral wool or an elastic foam, may be inserted in the airspace between the two sheets.
From an acoustic standpoint, such a two-leaf partition wall, whether or not it is lined with an insulating material, behaves at low frequency like a mass-spring-mass system in which the airspace or the filling of insulating material acts as the spring coupling the two sheets to one another. FIG. 1 shows how the sound reduction index (NF EN ISO 140-3) of such a two-leaf partition wall, with or without a filling of insulator, changes as a function of the frequency of the sound.
There is found to be a first characteristic weakness (f0) at low frequencies (approximately 100-150 Hz), referred to as the “breathing” frequency, corresponding to movements of the system in phase opposition, and a second characteristic weakness (fc) at high frequencies (between 2000 and 3000 Hz), referred to as the coincidence frequency, at which the wavelength of the incident sound wave “coincides” with the wavelength of the waves of flexing in the sheets.